Manufacture of alkyl carbonates



Aug. 9, 1927.

H. G. MITCHELL MANUFAGTURE 0F ALKYL CARBONATES Filed July 14. 1924 l w SLDNQRTF www. ma@ RSS: .Sk .aw maken..

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UNITED ys'1"..T 1-:s PATENT ol-Fica- HARRY GILBERT MITCHELL, OF BALTIMORE, MARYLAND, ASSIGNOR TO U. S. IND'US; TRIAL-ALCOHOL CO., A CORPORATION OF WEST VII`EtGII1'IA.v

MANUFACTURE OF ALKYL CARBONATES.

Application led Il'uly` 14,

My invention relates particularly to `a process for the manufacture of alkyl carbonates but especially those alkyl carbonates such, for example, as ethyl chlorocarbonate 5 and diethyl carbonate, and which is of such a character as to make the manufacture thereof commercially practicable so that the said product will be available for andl capable of use in the various arts. It is to be understood, also, that my processis applicable particularly to the production of alkyl car' bonates generally that are located in the same aliphatic series with diethyl carbonate.

'Ihe object of my invention is to provide a process for the production of alkyl carbonates, and particularly ethyl chlorocarbonate and diethyl carbonate, by means of which, if desired, the product may be produced continuously and in which there will be a high yield, while at the same time byproducts are recovered in an effective manner, thus preventing corrosion which would result from the escape of the same. A further object of my invention is to arrange the process in such a manner that a cheap source of supply otcarbon monoxide may be utilized therein. A further object is to conduct the process with the aid of phosgene gas formed from carbon monoxide and chlorine, in such a manner that the phosgene gas reacts with alcohol at low temperatures so as to minimize sideyreactions and losses resulting therefrom. Again, another object is to carry out the reaction between the phosgene and alcohol so that the ethyl chlorocarbonate first formed and the diethyl carbonate formed therefrom will be conducted continuously and without the previous separation of the ethyl chlorocarbonate, thus aid- -inAtheweconomical production of the diethyl carbonate'. A further object is to bring about the separation of the diethyl carbonate from the other materials contained in the resulting reaction mixture in an advantageous' manner and so as to obtain high yields by avoiding distillation with consequent hydrolysis and the formation of con- `r\--ni\itnt boiling mixtures vas far as possible.

' A``urther 'object of my invention will apy pear romheletaile description of the same hereinafter. g l

The three main reactions which take place laction is exothermic the chamber 8 is cooled@ 1924. `seran No. 725,835.v

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My invention` is capable of being carried out in many diierent ways but I have de# 6@ scribed only certain ways otcarrying out the same hereinafter and it is capable of belng carried out also in connection with manyv different types 'of apparatus but by way of illustration I have shown only one type of\ apparatus to be used in the accompanying drawings, in which- The figure isa diagrammatic representation of an apparatus yfor use in connection with my invention. v 7" In carrying out my invention I may provide any suitable source of carbon-monoxide to -be supplied by a tubel to a storage chamber 2 and thence by a tube 3 to a mixing tube 4. However, for this purpose I.prefer producer gas which would, for example, con tain 25 to 40% of carbon monoxide, 6() tc 65%,of nitrogen and small amounts of car bon dioxide, oxygen and hydrogen. Chlorine obtained from any suitable source of supply i -is fed by a tube `5 to a storage chamber and thence by a tube 7 to the mixing tube The gases from lthe tubes 3 and 7 are supplied at suchv a rate as to mix the chlorine and carbon monoxidevin vthe proportions oit "if mol for mol of the two gases. In order to obtain complete utilization of the chlorine an excess of the carbon monoxide amountu ing to 25% above the theoretical amount, is preferred. They are thence passed through a chamber 8 filled with -activated 'charcoal or bone-blackor providedfwith Some other appropriate catalyst. Inasmuch as the reby means of a water jacket 9. The temperature in the chamber 8 may ber observed byv means of a thermometer 10the temperature being kept below 250 C. in order to' avoid undesirable decomposition of the phosgene, althonghwit/ is to be understotgi that in the first stage ofthe reaction, thatis to say the first contact between the gases, thetemperature may exceed 250 C'. if desired withoutdetriment, but that preferably the.'

' v the catalytic chamber will not exceed 110o C.

scrubber 12 by a ltube 14.

lThe gases which leave the catalytic chamber 8, and comprising phosgene, inert gases and an excess of carbon monoxide, pass out by a tube 11 to the lower endof a scrubber 12 filled with glass beads which is supplied with a descending current of absolute alcohol from a tank 13 connected to the top of the The amount of alcohol fedl into the apparatus is preferably somewhat in excess ofbtwo mols of,y alcohol to one mol of phosgeue. Inasmuch as the reaction in the scrubber 12 between the alcohol and the phosgene gas and which results in the 'production of ethyl chlorocarbonate, exothermic, the scrubber 12 is also cooled by means of a .coiled pipe 15 ,therein provided for the passage of cooling water so thatthe temperature preferably is prevented from exceeding 40O C. In order to prevent the escape of any alcohol or hydrochloric acid from the top of the scrubber, a small scrubber 16 supplied with a current of water is provided/at the top ofthe scrubber 12 and connected thereto by means of a tube 17. A tube 18 at. the top of the s'crubber 16 permits any residual gases to pass o ut of the apparatus. The ethyl chlorocarbonate flows through a trapped tube 19 from the lower part of the scrubber 12 to a series of flasks 20, 21, 22 and 23, having baiies 23a and conf nected by overfiow pipes124, 25 and 26, while in a lperiod of from 4 to 5 hours the flask 23 is provided with a final overflow outlet pipe 27 for the diethyl carbonate. The firstflask 2D is preferably not heated as sufficient heat Yis provided by the contents of the flask but the other flasks 21, 22 and 23 are heated by burners 28A` 29 and 30 of any desired character. .The heating of the contents of' these flasks is carried out preferably and until the temperature reaches 82 to 85 C., which vis the final boiling point of the mixture, the

" V`51kconnected to the top of the asks 21, 22

temperature being observed by means of thermometers 31, 32, 33 and 34 contained in these fiasks. Any vapors formed in the flasks and which would-contain alcohol and hydrochloric acid, are rconveyed by a tube 35,

23, to a reflx',conderseifihi/gfwater cooling jacket 37 and the large amount of hydrochloric acid present is finally collected in a scrubber 38 connected by a tube 39 to the top of the condenser'36, the scrubber being filled with glassb'eads and supplied with a f/crrethof'water 39 for the absorption of the hydrochloric acid which passes out from the lower end lof the scrubber through av cape fromthe top of the Iscrubber by'neans of atube 41. l j vf The/diethyl carbonate coming. from the remove the impurities therefrom. This is va sodium chloride solution in water. upper aLi/,equaht treated in such a way as to preferably done by adding to the vsolution containing diethyl carbonate flowing from the tube 27, a neutralizing agent such, for example, as a solution of caustic potash in water, but preferably a 30% strength caustic soda solution in water, the water beingadded in this way in such solution neutral or slightly alkaline, and containing suicient water to dissolve any precipitated sodium chloride. .Preferably to counteract the heat of neutralization and to avoid hydrolysis of the diethyl carbonate due to increased temperatures, the mixture is cooled to from 10 to 30o neutralization and is agitated. The mixture is then allowed to separate into two layers, an upper ester layer containing approximately 80% diethyl carbonate and 20% alcohol, with slight impurities, and a lower layer which is comprised almostl entirelyrplf e layer `may then be decanted and, if desired, separated into its constituents by rectification. A

The above process may be modified somewhat, if desired, by changing the same to thc extent of introducing with the pho'sgene an amount of the alcohol equal vto 100% C. during the u conducting the process in this manner most A of the hydrochloric acid isA retained in the liquid.

Furthermore, in the purification ofL theA final product, whether-or not the 100% excess of alcohol has been introduced, the diethyl carbonate may be separated from the materials dissolved therein without pre- -vious neutralization', if desired, by1 the addition of water which will cause a separation of the liquid into two layers. For this purpose generally an amountJdf/watersisadded A toni/'times the volume of the diethyl carbonate solution, the amount of water, however, depending upon the concentration of the ester solution and being added in an. amount sufficient' to reduce the concentration of the alcohol solution formed to such a point that the esterlwill be most effectively carried intothe upper layer andY i the hydrochloric acid., completely retained clrobtaifled from the ester and alcohol solution wlll be reduced .in this way to a 10% i by the lowenlayer'. That is to say, the alco- '50 trapped pipe 40, and theresidual gases h solution of alcohol and water in the lower layer when sufficient, water has been added. A'gain, if desired, instead the ester and alcohol solutioncoming from the tube 27 may be purified with the aid ofv inert solvents including aromatic hydrocarbon solvents,

` suoli, for examp-le, as benz'ol,toluol or xylol solvent which is used will be such as to change the distribution of the ester in the mixture as to cause a separation to take place, forming an upper layer of ester and solvent solution containing all of the ester and a lower layer of dilute alcohol containing the hydrochloric acid. It is desirable,

therefore, that the solvent used shall bev a solvent for the alkyl carbonate, that the solution oftheester in the solvent be insolu-l ble in water and dilute alcohol solutions, that the solvent' be readily separable from the ester, that the hydrochloric acid be insoluble in the solvent and that the solvent be inexpensive and readily recoverable, although it is to be understood that the solvents to be used need not have all these characteristics.

While I have described my invention above in detail I wish it to be understood that man changes may be made therein without eparting from the spirit of the same. I claim:

1. The process which comprises forming phosgene from producer gas and chlorine with the aid of a cat-alyst. producing an alkylcarbonate from the phosgene and an aliphatic alcohol and eliminating the inert gases from the product.

" 2. The process `which comprises forming `phosgene from producer gas and chlorine with the aid of a catalyst, producing diethyl carbonate from phosgene and alcohol and eliminating the inert gases from the prod- Y uct.

"3. The process which comprises forming phosgene from producer gas land chlorine with the aid ofa catalyst. the amount of carbon monoxide in the producer gas being in excess of the theoretical quantity required to react with the chlorine, producing an alkyl carbonate from the phosgene'an'd -an aliphatic alcohol and eliminating the inert gases from the product. l

4. The process which comprises forming phosgene from producer, gas and chlorine with the aid of a catalyst, the amount of carbon'monoxide in the producer gas being in excess of the theoretical quantity required to react with thel chlorine, producing diethyl carbonate `from thev phosgene and alcohol and eliminating the inert gases fromi the product.v

5. The process which comprises forming phosgene. from producer gas and chlorine with the aid of a catalyst, the temperature being kept below 250o C., producing an alkyl carbonate from the phosgene and an aliphatic alcohol and eliminating the inert gases from the product;

6. The process which comprises forming phosgene from producer gas and chlorine with the aid of a catalyst, the temperature being kept below 250o C., producing vdiethyl carbonate from the phosgene and alcohol and eliminating the inert gases from the product.

7. The process which 4comprises continuously forming phosgene from carbon monoxide and chlorine, bringing the vapors into contact with a liquid aliphatic alcohol --so as to form a chlorocarbonate and heating the chlorocarbonate and an alcohol while continually carrying olf the dialkyl carbonate formed.

' 8. The process which comprises continuouslyforming phosgene from carbon monoxide 'and chlorine, bringing the vapors into cont-act with alcohol so as to form ethyl `chlorocarbonate and heating the ethyl chlodialkyl carbonate formed.

10. The process whlch comprises cont-in# uously forming phosgene `from carbon monoxide and chlorine, 4bringing the vapors into contact with alcohol so as t-o form ethyl chlorocarbonate and heating and refiuxing the ethyl chlorocarbonate and alcohol while continually carrying oif the diethyl carbonate formed.

`11. The process which comprises continuously forming an alkyl chlorocarbonate and heating the alkyl chlorocarbonate and a liquid aliphatic' alcohol while continually carrying off the dialkyl carbonate formed.

12. The process which comprises continuously-forming ethyl -chlorocarbonate and heatingithe'ethyl' chlorocarbonate and alcohol while continually carrying o' the diethyl carbonatel formed.

In testimony that I I havehereunto set my hand this of June, 1924.

HARRY GILBERT MITCHELL. y

3 'day claim the foregoing, 

